Human hepatocellular carcinoma (HCC) represents a major worldwide disease and is often associated with chronic hepatitis B virus (HBV) infection. In this proposal we will focus on three major aspects of HCC: 1) viral pathogenesis, 2) techniques for immunodiagnosis, and 3) development of antibodyconjugates for immunotherapy. In this regard we have developed a library of high affinity monoclonal antibodies directed against distinct and separate determinants present on human hepatoma cells. Such reagents will be used to develop in vitro and in vivo reagents for immunodiagnosis. Indeed, one such antibody, namely P215457 recognizes a 50 kd (P50) cell surface protein present on both human and rat hepatoma cell lines as well as human hepatoma tissue; this antigen appears relatively restricted to transformed hepatocytes and was not detected in normal human tissues. The Fab fragment of P215457 has been prepared and radiolabeled with (131I). Based on in vivo nuclear imaging studies in a nude mouse system, we now believe that this reagent is suitable for detection of HCC in man. The physical and molecular characteristics of P50 will be studied in greater detail. It is noteworthy that a new library of 124 monoclonal antibodies have neen produced to affinity purified P50. We now plan to search for this antigen and other similar antigens in serum of patients with multisite monoclonal radioimmunoassays (M-RIAs). Therefore it is our goal to provide immunodiagnostic techniques which will detect HCC at an early stage when the tumors may be surgically resectable. Recent in vitro and in vivo investigations suggest that these monoclonal antibodies may have value in the treatment of HCC. We will extend and consolidate these findings and covalently link the monoclonal antibodies to cytotoxic agents such as adrimycin and isotopes such as (131I). Finally, our recent studies suggest the presence of HBV or HBV "variants" in some seronegative (by conventional assays) patients with HCC. Thus we will further explore the role of HBV in the development of HCC using a recently developed second generation antiHBs RIA. The assay is capable of detecting as little as 15 pg/ml of HBsAG-associated epitopes in serum. The studies will also include affintiy purification and structural analysis of antigens by a newly developed technique designated signature analysis. We are optimistic that such studies will provide new information on the viral pathogenesis of HCC.